Prior work regarding glycolysis of PET and PET bottle flakes to BHET/Oligomers are disclosed in a number of Patents viz., EP 0926178, EP 1153070, EP 0966344, U.S. Pat. No. 646,322, U.S. Pat. No. 5,635,584 etc. However most of these relate to separation of BHET, its purification and repolymerization to PET or direct extrusion.
JP 2001-316327 describes a process for producing oligomers by subjecting PET and MEG to a depolymerization reaction in the presence of depolymerization catalysts. This patent claims a method to produce ester oligomer from PET using a depolymerization catalyst. Whereas in the present invention, complete depolymerization of the flakes by glycolysis/depolymerization are not carried out.
N.Z. Patent 0517832 discloses a process for preparing food contact PET resin from waste PET containers. The process comprises producing clean flakes by washing, rinsing and drying the flakes and subsequently melting the flakes and extruding it to form strands which are cut into granules. Unless carefully controlled this process has the disadvantage of degradation of PET while extruding a high molecular weight PET. In addition, in the instant process foreign impurities are not removed.
U.S. Pat. No. 5,554,657 describes a process for recycling PCR. However the method is for mixed PCR containing polymers from which PET is selectively dissolved and separated by a solvent. From this solution PET is separated, cleaned, combined with virgin PET and further processed by polymerization to the required high molecular weight polymer. In this process the quality of the products is not to the desired standards.
U.S. Pat. No. 6,350,851 deals with producing high purity BHET from PET flakes by a glycolysis procedure. The purified BHET is then polymerized by using Sb2O3 and GeO2 as combination catalysts. It is obvious that this process is for 100% recycle of PCR and that too by separating the BHET and subsequently polymerizing which involves more steps. In this work the depolymerized material consisting of MEG+BHET was decolorized with activated carbon. This solution was subsequently deionized with anion-cation exchange resin. The deionized solution was then charged into an autoclave for polymerization. So it is obvious at each stage the BHET is separated and processed.
U.S. Pat. Nos. 6,263,294, 5,539,078, 5,594,092, 5,612,423, 5,895,807, 4,609,680 and 4,020,049 all deal with prepolymer heel in the process of making PET. However these disclosures mainly deal with virgin PET or PEN polymers and not with recycle of PCR.
U.S. Pat. No. 5,876,644 deals with a process of directly extruding PRC flakes to a low molecular weight melt and blending this melt with a melt of virgin polyester prepolymer to get a blended prepolymer which is subsequently solid state polymerized. In this process there is no glycolysis of the flakes. The flakes are melted as such in an extruder to a slightly lower molecular weight material. This material is then blended with virgin melt and polymerized further. This process is a direct extrusion of flakes wherein the flakes are not reacted with any chemical.
U.S. Pat. Nos. 6,410,607, 6,162,837, 5,223,544, 4,368,274 and 4,118,187 disclose PET scrap utilization to produce PET. These disclosures do not deal with the simultaneous process of recycling PCR flakes along with virgin RM viz. PTA, IPA and MEG.